Production of homozygous s₁ seedlings for s gene in 'hirado buntan' pummelo (citrus grandis osbeck) and determination of the s alleles (s₉and s₁₀) by pollination with the s₁ seedlings to citrus cultivars

Gametophytic self-incompatibility (SI) in Citrus is known in pummelo, mandarin and many hybrid cultivars with pummelo in their pedigrees. What seems to be lacking, however, is determination of allelic variation in SI gene (S) and the genotypes of self-incompatible and semi self-incompatible cultivare. In previous studies, S genotypes of several Citrus cultivare were estimated on the basis of segregation distortion for Got-3 gene in F₁ progenies between these cultivars. In this study, S₁ seedlings were produced from selfpollinated 'Hirado Buntan' pummelo, and homozygous S₁ seedlings for the S gene were determined by the pollination with 'Hirado Buntan'. Then, the homozygous S₁ seedlings were pollinated with the homozygous S₁ seedling (S_aS_a) each other and classified them into two genotype groups of S_aS_a and S_bS_b. The ten cultivars, whose S genotypes were predicted on the basis of joint segregation analysis with Got-3 gene in their progenies, were pollinated with the homozygous S₁ seedlings (S_aS _a or S_bS_b). Pollen tube behavior in the style of the ten Citrus cultivars after pollination with the S_a or S _b pollen led to the conclusion that 'Hirado Buntan' has S₉ and S₁₀ alleles. Furthermore, pollen tube arrest in the style of self-compatible 'Kabusu' sour orange pollinated with S₉ pollen suggested that the genotype of 'Kabusu' is S_jS₉. Inscrutably, neither S₉ nor S₁₀ alleles were found in a group belonging to the Hirado pummelo line, which started from seeds sown by the 11th feudal load Terasu Matsura of the domain of Hirado. This fact supported the two origins of Hirado pummelo plants described in the literature, and indicated the association of multiple seed and/or pollen parents with different S alleles to the original seed production.